Effect of Adrenocorticotropic Hormone on Plasma Glucocorticoids and Antidiuretic Hormone of Cattle Exposed to 20 and 33 C

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Abstract
Four open, dry Holstein cows in the University of Missouri [USA] Climatic Laboratory were used to study the effect of ACTH administration on glucocorticoids and antidiuretic hormone [ADH] of plasma in 2 reversal trials at thermoneutral (20.degree. C, 50% relative humidity) and heat (33.degree. C, 50% relative humidity) conditions. Average glucocorticoids (saline vs. ACTH) at thermoneutrality were 8.3 and 41.2 ng/ml while values for heat were 6.2 and 40.4 ng/ml. The effect of heat on glucocorticoids of plasma was not significant. Injection of ACTH under thermoneutrality and heat caused a marked increase in ADH within 5 min which lasted to 120 min. At thermoneutral average ADH levels (saline vs. ACTH) were 0.5 and 1.9 pg/ml while values for heat were 1.8 and 3.6 pg/ml. ADH concentrations under heat were higher than under thermoneutrality in cows injected with saline and ACTH. The fast response of ADH of plasma to exogenous ACTH suggests that ACTH might act directly at higher levels of the CNS causing release of ADH.

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